Encapsulated weighing cell with eccentric load error adjustment

Abstract

A gravimetric measuring instrument has a weighing cell and a flexible, tubular-shaped encapsulation. The weighing cell has a parallel-guiding mechanism and at least one measurement transducer. The ends of the encapsulation are attached, respectively, to the stationary parallelogram leg and the movable parallelogram leg, so that at least the parallel-guiding mechanism and the measurement transducer are enclosed by the encapsulation, protecting them from dirt and humidity. In some aspects, the parallel-guiding mechanism has an adjustment region formed at one of the parallelogram legs which allows adjustment of the distance between at least one flexure pivot of the upper parallel-guiding member and a flexure pivot of the lower parallel-guiding member. This adjustment region is mechanically connected to at least one adjustment-setting area, which is arranged outside the encapsulation and allows changes to be made to the adjustment region.

What is claimed is: 
     
       1. A gravimetric measuring instrument, comprising:
 a weighing cell, comprising:
 a parallel-guiding mechanism, which includes a movable parallelogram leg, a stationary parallelogram leg, and upper and lower parallel-guiding members, each of the parallel-guiding members joined to each of the parallelogram legs at a flexure pivot, so that the parallel-guiding members guide vertical movement of the movable parallelogram leg and connect the respective parallelogram legs; and 
 a measurement transducer; 
 
 a flexible tubular-shaped encapsulation, one end of which is attached to the stationary parallelogram leg and the other end of which is attached to the movable parallelogram leg, so that at least the parallel-guiding mechanism and the measurement transducer are enclosed by the encapsulation and thereby protected against dirt and humidity; 
 an adjustment region, formed at at least one of the respective parallelogram legs, the adjustment region allowing adjustment of a distance between at least one of the flexure pivots of the upper parallel-guiding member and one of the flexure pivots of the lower parallel-guiding member, and 
 an adjustment-setting area, arranged outside the encapsulation and mechanically connected to the adjustment region, to allow changes to be made thereto. 
 
     
     
       2. The instrument of  claim 1 , further comprising:
 a deformation zone in the adjustment region, constituted by at least one cutout that horizontally traverses the parallelogram leg on which the adjustment region is situated, the deformation zone also defining a pivot axis, such that:
 upon applying a force or a torque, the adjustment region tilts about the pivot axis, which is oriented in a transverse direction of the parallel-guiding mechanism; and, 
 as a result of the tilting, the end of the parallel-guiding member that terminates in the adjustment region is permanently displaced in a vertical direction, correcting an eccentric load error in a lengthwise direction of the parallel-guiding mechanism. 
 
 
     
     
       3. The instrument of  claim 2 , wherein:
 applying an adjusting force or adjusting torque to the adjustment-setting area subjects the deformation zone to a controlled plastic deformation; and 
 a targeted permanent position-adjustment of the parallel-guiding members relative to each other is accomplished through the controlled plastic deformation. 
 
     
     
       4. The instrument of  claim 3 , further comprising:
 an additional cutout that splits the adjustment region at the vertically adjustable end of the parallel-guiding member that terminates in the adjustment region, the additional cutout running in a vertical lengthwise median plane of one of the parallelogram legs and extending up to the flexure pivot, forming two separate adjustment regions with separate deformation zones that are adjacent to each other, so that:
 when parallel forces or torques are applied to the two adjacent separate adjustment regions and parallel tilt displacements are imparted thereby, a permanent parallel vertical adjustment of the flexure pivot occurs, correcting an eccentric load error in the lengthwise direction of the parallel-guiding mechanism, and 
 when anti-parallel forces or torques are applied to the two adjacent separate adjustment regions and opposite tilt displacements are imparted thereby, a permanent twisting distortion of the adjustable end of the parallel-guiding member occurs, correcting an eccentric load error in the transverse direction of the parallel-guiding mechanism. 
 
 
     
     
       5. The instrument of  claim 4 , further comprising:
 a perforation of the flexure pivot, or a continuation of the additional cutout up to the parallel-guiding member, at the vertically adjustable end of the parallel-guiding member that terminates in the adjustment region, resulting in two separate adjacent flexure pivots. 
 
     
     
       6. The instrument of  claim 5 , further comprising:
 a knee lever comprising two knee lever members that are pivotally connected at one end to each other through a knee joint, with the other end of each knee lever member located near the flexure pivots and pivotally connected to the parallelogram leg that includes the adjustment region of which the knee lever is a part, and 
 a transmitting element, through which the adjustment-setting area is connected to the knee joint. 
 
     
     
       7. The instrument of  claim 6 , wherein:
 the distance between the flexure pivots of one of the parallelogram legs, in the non-adjusted state, is larger than the distance between the flexure pivots of the other parallelogram leg. 
 
     
     
       8. The instrument of  claim 7 , wherein:
 the adjustment-setting area comprises one of:
 a blind hole for engaging an adjustment tool; 
 a suitable surface formation for engaging a screw driver or wrench; 
 an adjustment screw, or 
 an adjustment wedge. 
 
 
     
     
       9. The instrument of  claim 1 , wherein:
 the flexible tubular-shaped encapsulation comprises:
 a first end portion, with a gas-tight connection between the first end portion and the movable parallelogram leg; 
 a second end portion, with a gas-tight connection between the second end portion and the stationary parallelogram leg; and 
 a tubular-shaped mid-portion, with a gas-tight connection between the mid-portion and the respective end portions. 
 
 
     
     
       10. The instrument of  claim 9 , wherein:
 the deformation zone is located in a plane which contains one of the encapsulation end portions. 
 
     
     
       11. The instrument of  claim 9 , wherein:
 at least one of the end portions comprises a flexible corrugation. 
 
     
     
       12. The instrument of  claim 1 , wherein:
 the encapsulation comprises rubber, synthetic material, or stainless steel. 
 
     
     
       13. The instrument of  claim 1 , wherein:
 the encapsulation comprises a mid-portion configured in the form of a bellows. 
 
     
     
       14. The instrument of  claim 2 , further comprising:
 an additional cutout that splits the adjustment region at the vertically adjustable end of the parallel-guiding member that terminates in the adjustment region, the additional cutout running in a vertical lengthwise median plane of one of the parallelogram legs and extending up to the flexure pivot, forming two separate adjustment regions with separate deformation zones that are adjacent to each other, so that:
 when parallel forces or torques are applied to the two adjacent separate adjustment regions and parallel tilt displacements are imparted thereby, a permanent parallel vertical adjustment of the elastic flexure pivot occurs, correcting an eccentric load error in the lengthwise direction of the parallel-guiding mechanism, and 
 when anti-parallel forces or torques are applied to the two adjacent separate adjustment regions and opposite tilt displacements are imparted thereby, a permanent twisting distortion of the adjustable end of the parallel-guiding member occurs, correcting an eccentric load error in the transverse direction of the parallel-guiding mechanism. 
 
 
     
     
       15. The instrument of  claim 4 , further comprising:
 a knee lever comprising two knee lever members that are pivotally connected at one end to each other through a knee joint, with the other end of each knee lever member located near the flexure pivots and pivotally connected to the parallelogram leg that includes the adjustment region of which the knee lever is a part, and 
 a transmitting element, through which the adjustment-setting area is connected to the knee joint. 
 
     
     
       16. The instrument of  claim 1 , wherein:
 the distance between the flexure pivots of one of the parallelogram legs, in the non-adjusted state, is larger than the distance between the flexure pivots of the other parallelogram leg. 
 
     
     
       17. The instrument of  claim 1 , wherein:
 the adjustment-setting area comprises one of:
 a blind hole for engaging an adjustment tool; 
 a suitable surface formation for engaging a screw driver or wrench; 
 an adjustment screw, or 
 an adjustment wedge. 
 
 
     
     
       18. A gravimetric measuring instrument, comprising:
 a weighing cell, comprising:
 a parallel-guiding mechanism, which includes a movable parallelogram leg, a stationary parallelogram leg, and upper and lower parallel-guiding members, each of the parallel-guiding members joined to each of the parallelogram legs at a flexure pivot, so that the parallel-guiding members guide vertical movement of the movable parallelogram leg and connect the respective parallelogram legs; and 
 a measurement transducer; 
 a flexible tubular-shaped encapsulation, enclosing at least the parallel-guiding mechanism and the measurement transducer, comprising:
 a first end portion attached to the movable parallelogram leg and providing a gas-tight connection therebetween; 
 a second end portion attached to the stationary parallelogram leg and providing a gas-tight connection therebetween; and 
 a tubular-shaped mid-portion, providing a gas-tight connection between itself and each of the end portions; 
 wherein at least one of the end portions comprises a flexible corrugation; 
 
 
 an adjustment region, formed at at least one of the respective parallelogram legs, the adjustment region allowing adjustment of a distance between at least one of the flexure pivots of the upper parallel-guiding member and one of the flexure pivots of the lower parallel-guiding member, wherein the distance between the flexure pivots of one of the parallelogram legs, in a non-adjusted state, is larger than the distance between the flexure pivots of the other parallelogram leg; and 
 an adjustment-setting area, arranged outside the encapsulation and mechanically connected to the adjustment region, to allow changes to be made thereto.